An example of a virtual world is a digital terrain model (DTM). A DTM comprises a digital raster grid that divides a land surface of constant elevation into a plurality of grid cells with each cell holding a separate elevation value. DTM have a variety of applications including, for example, radio propagation studies conducted by telecommunications companies to assess where wireless signals reach and where they are blocked or reflected.
Many virtual worlds/models employ clutter data which is stored in a database (a “clutter database”). For each point or coordinate of the virtual terrain, there is a code to a look-up table which indicates that at the given point or coordinate there is a particular type of object, such a tree/forest, parking lot, river, or building. Elevation data may be absent from clutter data or absent from the virtual models which are presented to users with a VR or AR output device using the clutter data. In some cases it may be that clutter data oversimplifies the characterization of elevations. For instance, terrain coordinates labeled with “dense forest” may be given a uniform 60 feet elevation value despite the fact some parts of the forest are higher in elevation and some parts are lower in elevation. As another example, a user would see in the VR or AR output an indication that a building exists at some location, but the building would be entirely flat and conforming with the terrain. In other words, the representation would be essentially two-dimensional (2D) and the building would have no elevation or height representation whatsoever. Sometimes a provider of the virtual model has access to elevation data but denies access to users. In some cases, a fee system is used to limit access to elevation information for a virtual model. If a user has need of elevations for only a small part of the model, the user may be forced to pay for elevation data for the entire model or a larger part of the model than is needed.
An existing solution by which virtual world providers (e.g., Google® which offers Google Earth®) determine elevation dimensions for objects such as buildings or forests is to use satellite images, aerial images captured from aircraft, or a combination of the two. Stereo imagery is the practice by which images of the same object taken from two different camera locations are used to determine elevation. A difference in apparent location of the object will appear between the two images. This is called parallax. The measured parallax together with the known camera locations are used together to determine a true elevation of the object. A problem with the aerial approach is that it is expensive and inconvenient. Satellites and planes are very expensive to obtain, operate, and maintain, yet they are essential to existing stereo imagery methods for determining elevations. The need exists for new cost effective solutions for determining elevations for virtual models of real world spaces.